For cable video services, specific video programs are typically broadcast on the cable in their own dedicated frequency band. Any TV in the house can be tuned to any specific program by tuning to that frequency. In the case of newer TV services (e.g., satellite TV distribution, internet TV distribution), programs are “tuned” in a master STB and are then distributed to remote STBs over a home network. In many cases, a home network (or home distribution system) needs to be installed. Although wires (coax, twisted pair, etc.) are reliable, they can be expensive to install and homeowners may not like installers drilling through walls for the installation. With that in mind, the industry is interested in wireless solutions to the video program redistribution system problem.
Most existing in-home digital video distribution systems use Ethernet as the distribution media. Since most Ethernet installations use at least 100 Mbps link rates and use switches, which selectively transmit traffic only to the branch containing the addressed device, there are very few QoS issues when used in a video redistribution system with controlled traffic rates. There could be problems with Ethernet if one transmitted general IP data traffic on the same network without some type of QoS protection. There is currently one type of media access control (MAC) level QoS available for Ethernet. It is a priority based scheme, which uses the user priority field in the virtual local area network (VLAN) tag. The addition of parameterized QoS (bandwidth request, bandwidth guarantee, admission control, etc.) is currently the subject of one of the working groups within the IEEE 802.1 subcommittee on IEEE 802 network bridging. However, Ethernet has the disadvantage that it requires wires to be run and it is desirable to have a no-new-wires installation technology.
What is needed is a wireless distribution system that can replace the Ethernet distribution through MAC-level bridging. Many home networks distribute the video using IP protocols, but there are many possibilities. In some cases video is sent using UDP as specified by real time transport protocol (RTP), while in other cases (e.g., Digital Living Network Alliance (DLNA)) video is distributed over TCP. UDP requires only one way communication while TCP requires two-way communication. There are additional possibilities. It would be desirable to have a home distribution system that does not require any modifications to the master and remote devices/STBs when they already have an Ethernet interface (i.e., no bandwidth reservation, no talking to the wireless bridge devices, etc.). It is also desirable that the MAC layer be extremely efficient since the media is wireless and therefore a band-limited common media. For that reason, the present invention uses a TDMA MAC scheme. In a TDMA MAC scheme, time allocations are assigned resulting in dedicated bandwidth to each client/remote device (STB): As used herein, “/” indicates, alternative names for the same component. Since the multi-media traffic is mostly downstream from the master device to a few remote devices, there is an opportunity to eliminate overhead (preamble, PHY header, InterFrame Spacing) due to multiple PHY packets in each time allocation thereby increasing network efficiency and increasing the available net bit rate.
IEEE 802.11N, which is currently under standardization in the IEEE is being touted as a means for video distribution. There are a number of concerns with the technology that is the subject of IEEE 802.11N. First, it still is based on CSMA (IEEE 802.11). This type of MAC layer is inherently inefficient and provides no QoS guarantees. Although many MAC-level QoS enhancements are being added to IEEE 802.11N, it is unlikely that a CSMA based MAC can be as efficient as a TDMA MAC. QoS enhancements include the priority based QoS from IEEE 802.11E, some form of polling and the addition of MAC Service Data Unit (MSDU) and MAC Protocol Data Unit (MPDU) aggregation. The final method of aggregation has not been chosen yet. There have been several proposals, all different than the method described here. These enhancements can be very useful in managing the resources of an IEEE 802.11 network, but do not make any QoS guarantees that are necessary or desirable for wireless home video distribution systems. The polling could be used to create TDMA-like services on which the present invention could operate, but the polling itself cuts into the MAC efficiency. MAC efficiency is even more critical for a wireless network because of the limited link rate available to the more remote areas of a house. Most current Wireless LANs utilize a common transmission media (i.e., wireless spectrum at the same transmission frequency). Because of that, the MAC needs a mechanism for sharing that media. It should be noted that once a transmission opportunity is acquired (via CSMA) or assigned (via polling) the present invention could be employed.
IEEE 802.16 also contains a form of MPDU aggregation using a MAP at the beginning of the SuperMAC frame that indicates where the separate MPDUs start. IEEE 802.16 also includes a method of aggregating MSDUs using subheaders. Both methods increase the efficiency of an IEEE 802.16 link, but require that MPDUs start on PHY character boundaries. This implies more cooperation between the MAC and PHY layer than is desirable.
Some service providers are looking at no-new-wire technologies based on coax, phone lines, and/or power lines. There are many different possibilities, most of the possibilities have some form of priority or parameterized QoS. The problems inherent with these solutions are that even though there may be coax or phone lines already in a house, those lines still may not be wired to the right spot or may be a topology that is difficult for the technology to handle. Most of these technologies also share bandwidth with other houses (e.g., power lines for up to 4 houses are on one power transformer) and currently lack reliability. For the parameterized service, the STB must know how much bandwidth to reserve for each link. For a video home distribution system, the traffic is not under control, may be bursty, and is at least partially unknown.
The present invention encompasses a home multi-media stream distribution system that solves the problems highlighted above.